A. Field of the Invention
This invention relates in general to automatic calibration devices for push-pull and related cables.
B. Description of the Prior Art
Various types of cables have been used in automotive applications for many years to transfer motion from one controlling member to another member to be controlled at a remote location, such as from the accelerator to the carburetor, from the gear shift to the transmission, from levers and knobs on the dash panel to the hood, trunk and other latches, etc. These cables generally have an interior core wire and a surrounding sheath, and are known as push-pull cables. The core wire is attached to the controlling member at one end and to the controlled device at the other to do the actual work. The sheath is also secured at both ends and acts as a guide for the core wire.
Many of the applications in which these cables are used are merely release or tighten operations that do not require close tolerances or adjustment of the cables. Some applications, however, do require a close tolerance; such as from the accelerator to the carburetor, from the gear shift to the transmission and in the heater-air conditioning blend door operation. Such close tolerance applications require that the cables be calibrated to exactly align the input and output. Several manual and automatic calibration systems have been used for this purpose, but are not entirely adequate for various reasons.
The simplest means of manual calibration is to slot the sheath at one end so that the sheath can be moved back and forth to take up or release the cable length as required. In such calibration the adjustment is done after the core wire and the non-slotted sheath end are attached. Another type of manual calibration system is to use a turnbuckle adjuster, located in the middle of the sheath, so that the sheath length may be altered to make the necessary calibration.
One type of automatic system uses outer loops of Bowden cables and a special clip that allows the loops of the cable sheath to slip by the clip and align under a one-time calibration load. Another automatic system uses a slip device in place of the turnbuckle adjuster of the manual system described above. A third automatic system is used in aligning the cable between the heater control temperature lever on an automotive dash and the water control valve. In this system, the bell crank arm of the water valve is attached to the cable core wire by means of a special slip clip. The cable is attached to the heater control temperature lever in the normal manner. The connections are made such that when the heater control temperature lever is moved the water valve bell crank arm will hit its associated stop before the heater control temperature lever hits its stop. Calibration is then achieved by forcing the heater control temperature lever to its stop while the water valve bell crank arm is resting against its stop, causing the cable core wire to move in the special slip clip, and thereby setting the correct length of cable between the two points for further normal operation.
Each of the above systems is unsatisfactory for various reasons, such as high cost, inaccurate calibration, difficulty of installation, complexity, etc.